The present disclosure relates generally to communications systems and, more particularly, to a codebook based interference alignment scheme for use in a wireless communication system.
One of the major challenges in wireless communication systems is to overcome interference caused by other users, such as when a mobile device in cellular systems receives interfering signals from multiple transmitters. Traditional schemes attempt to manage interference as noise or by orthogonalizing channel resources between different transmitters (base stations or access points) by assigning different frequency channels, time slots, or codes to different resources (e.g., frequency division multiple access (FDMA)/time division multiple access (TDMA)/code division multiple access (CDMA)). In addition, concurrent transmission techniques (interference alignment (IA)) have been proposed in which multiple senders jointly encode signals to multiple receivers so that interference is aligned and each receiver is able to decode its desired information.
Interference alignment provides better performance than orthogonalization-based schemes by aligning the interference at a receiver coming from different sources in the least possible spatial dimensions to maximize the number of interference-free dimensions, thus providing more degrees of freedom for signal transmission and improving the throughput performance. With interference alignment, a transmitter can partially or completely “align” its interference with unused dimensions of the primary terminals, thereby maximizing the interference-free space for the desired signal in an interference channel. For example, it has been shown that all the interference can be concentrated roughly into one half of the signal space at each receiver, leaving the other half available to the desired signal and free of interference. When considering sum capacity for n users in the high SNR regime, the sum capacity for each transmitter scaling as n/2 log(SNR) is achievable which is equivalent to n/2 degrees of freedom for the sum capacity for each transmitter. Moreover, for fixed SNR values, the sum capacity achieved by interference alignment has been shown to scale linearly with n.
A significant challenge with existing interference alignment schemes is that they require perfect global channel knowledge about all channels in the network, which in turn imposes significant feedback overhead and coordination between nodes. In addition, existing interference alignment schemes are highly sensitive to channel estimation and quantization error, antenna configuration, and mobility.